Improvement of Phase‐Change Memory Performance by Means of GeTe/Sb₂Te₃ Superlattices

Abstract

GeTe/Sb2Te3 superlattices (SLs) obtained by sputtering are integrated in phase‐change memory (PCM) devices with a “wall structure”. The high structural quality of SLs deposited on TiN or SiNx layers, used as metallic bottom heater and dielectric bottom layer in PCM devices, is established by X‐ray diffraction, for as‐grown SLs and after an annealing corresponding to the maximum thermal budget during the integration process. Scanning transmission electron microscopy (STEM) images of SLs within PCM cells confirm that the SL structure is kept after integration. A robust statistical analysis on a large number of devices demonstrates unambiguously that the RESET current is lower in SL devices than in GeTe reference devices and decreases when the Sb2Te3 layer thickness in the SL increases from 2 to 8 nm. STEM imaging of a PCM cell incorporating an SL demonstrates that switching from the low‐ to the high‐resistance state occurs through a melting–quenching process and is not due to crystal–crystal transition or defect reorganization in the SL, in contrast to what is commonly stated in the literature on interfacial phase‐change memories (iPCMs). The origin of the improved switching performance of SL‐based PCM devices is discussed, linked with the impact of swapped bilayers.

Atomic Layer Deposition of Sb2Te3/GeTe Superlattice Film and Its Melt‐Quenching‐Free Phase‐Transition Mechanism for Phase‐Change Memory

“…Subsequent studies, however, revealed a crystalline-to-amorphous phase-transition behavior in a similar SL structure, indicating the possible controversy in the switching mechanism. Different mechanisms such as enhanced thermal efficiency, [10][11][12][13][14] stacking fault [15] or strain-assisted transition, [16,17] and partial amorphization [18] have also been suggested in more recent works. Still, studies so far lack a detailed analysis of the crystalline state in the set state.Besides, in previous studies, physical growth methods, such as sputtering and molecular beam epitaxy used to grow the SL films, cannot grow conformal film on highly topographical surfaces.…”

Innovative Nanocomposites for Low Power Phase‐Change Memory: GeTe/C Multilayers

“…[5,6] Note that [(GeTe) 4 nm /C 1 nm ] 10 has similar performance as the so-called "interfacial Phase-Change Memories" (iPCM) in terms of RESET current reduction. [16,17] Thus, ML devices annealed at 425 °C show promising properties in terms of I RESET reduction for the development of high-density PCMs.…”

In‐Plane Twinning Defects in Hexagonal GeSb2Te4

“…[ 34–38 ] Conventional thermal‐based transitions were reported in superlattice devices. [ 39,40 ] However, quasi‐2D amorphization in the superlattice is unlikely due to the close melting temperature of GeTe and Sb 2 Te 3 (≈100 °C), which was corroborated by ab initio molecular dynamics simulations. [ 41 ] Partial amorphization was instead achieved in TiTe 2 /Sb 2 Te 3 phase‐change heterostructures, [ 42–45 ] because of the large difference in melting temperature (>500 °C) between the two constituting alloys.…”